Petrogenesis of the Early Carboniferous Alasitan diorites from the northern margin of Yili Block and implication for subduction process of the North Tianshan Ocean

There are massive Carboniferous magmatic rocks in the northern Yili Block.However, rare middle-late Early Carboniferous (340~320 Ma) magmatic rocks were reported, which limited our understanding for the tectonic evolution of the northern Chinese West Tianshan of this period.In order to constrain the tectonic setting of the northern Yili Block, we conducted detailed petrology, geochemistry, zircon U-Pb dating and Lu-Hf isotope analyses on a newly identified middle Early Carboniferous dioritic pluton along the Alasitan river in the northern Yili Block.Microgranular dioritic enclaves are widely developed within the diorites.The two types of rocks display different evolutionary trends in multiple bivariate diagrams of major and trace elements, indicating different petrogenesis and magma sources.Both types of rocks are enriched in LILEs, depleted in HFSEs (Nb, Ta, Ti), which are characteristics of magmatic arc rocks.Combined with regional geology, we suggested that the northern Yili Block experienced regional extension since the middle-late Early Carboniferous, which might be related to the slab roll back or retreat of the North Tianshan oceanic crust.